This paper presents an adapted anion exchange column chemistry protocol which allowed separation of high‐purity fractions of Cu and Zn from geological materials. Isobaric and non‐spectral interferences were virtually eliminated for consequent multiple‐collector ICP‐MS analysis of the isotopic composition of these metals. The procedure achieved ∼ 100% recoveries, thus ensuring the absence of column‐induced isotopic fractionation. By employing these techniques, we report isotopic analyses for Cu and Zn from five geological reference materials: BCR‐027 blende ore (BCR), δ65Cu = 0.52 ± 0.15‰ (n = 10) and δ66Zn = 0.33 ± 0.07‰ (n = 8); BCR‐030 calcined calamine ore (BCR), δ66Zn = ‐0.06 ± 0.09‰ (n = 8); BCR‐1 basalt (USGS), δ66Zn = 0.29 ± 0.12‰ (n = 8); NOD‐P‐1 manganese nodule (USGS), δ65Cu = 0.46 ± 0.08‰ (n = 10) and δ66Zn = 0.78 ± 0.09‰ (n = 9); SU‐1 Cu‐Co ore (CCRMP), δ65Cu = ‐0.018 ± 0.08‰ (n = 10) and δ66Zn = 0.13 ± 0.17‰ (n = 6). All uncertainties are ± 2s; copper isotope ratios are reported relative to NIST SRM‐976, and zinc isotope ratios relative to the Lyon‐group Johnson Matthey metal (batch 3‐0749 L) solution, JMC Zn. These values agree well with the limited data previously published, and with results reported for similar natural sample types. Samples were measured using a GVi IsoProbe MC‐ICP‐MS, based at the Natural History Museum, London. Long‐term measurement reproducibility has been assessed by repeat analyses of both single element and complex matrix samples, and was commonly better than ± 0.07‰ for both δ66Zn and δ65Cu.
The modified sample-standard bracketing method (m-SSB) combines a sample-standard bracketing and an inter-element correction procedure to account for instrumental mass fractionation during multi-collector ICP-MS measurements. Precisions for Cu and Zn isotopes in plant and experimental granite leachate samples are in line with those obtained using other mass bias correction techniques. In addition, the inherent temporal drift of mass bias during the analytical session and the empirical linear relationship between dopant and analyte are used to apply independent correction schemes that rigorously check the accuracy of data obtained by m-SSB. Consequently, a very robust isotope data set is obtained. We further suggest the use of a matrix-element spike in inter-element doped standards to increase the mass bias variability. This improves the quality of the empirical relationship between dopant and analyte and enables crosschecking of the m-SSB method when instrumental mass bias is stable.
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